1. Field of the Invention
The present invention relates to an extrusion device for extruding highly viscous material such as an adhesive agent, a gap-filling material, an adhesive gap-filling material, grease and so on from a tubular container to apply it to an object. More particularly, it relates to an extrusion device which prevents undesirable discharge of the viscous material from the nozzle.
2. Description of Prior Art
Caulking guns and grease guns have been known as devices for extruding highly viscous material from a tubular container. For instance, a caulking gun, which is used for filling a gap or a joint portion in panels and building materials for buildings and containers with a highly viscous liquid gap-filling material or an adhesive gap-filling material by extruding it from a tubular container, is disclosed in Japanese Examined Utility Model Publications 31013/1971 and 11964/1980. The caulking gun is constructed in such a manner that a tubular container containing a viscous gap-fitting material is formed integrally with the main body or a cartridge type tubular container is fitted to the main body and a push rod is supported by the main body so as to be slidable along the axial direction of the main body, wherein the gap-filling material in the tubular container is extruded from a nozzle formed at the front end of the tubular container by a piston member attached at the end of a push rod when the push rod is urged in one direction along the axial direction.
A driving unit as means for urging the push rod generally comprises a driving piece formed of a plate-like body in which an opening having a diameter slightly greater than the outer diameter of the push rod is formed, the driving piece being supported by inserting the push rod in the opening so that it is slidable in the axial direction and inclinable with respect to the axial direction of the push rod, a coil spring interposed between the main body of the extrusion device and the driving piece and wound around the outer circumferential part of the push rod so that the driving piece is pushed in the opposite direction opposite the forwarding direction of the push rod, and a lever pivotally supported by the extrusion device main body which pushes an end of the driving piece in the forwarding direction of the push rod when the lever is operated.
The operation of the driving unit is such that when an end of the driving piece is pushed by turning the lever in one direction, inclination of the driving piece is caused with respect to the push rod whereby a circular edge portion of the opening is frictionally engaged with the outer circumference of the push rod. Namely, the push rod is pushed together with the driving piece against the spring action of the coil spring.
The conventional extrusion device is provided with a control means for controlling the push rod. The control means generally comprises a control piece in which a control opening having a diameter slightly greater than the outer diameter of the push rod is formed, the push rod being inserted in the control opening and one end of the control piece being turnably supported by a supporting plate made of a plate-like material projecting from the extrusion device main body, and a coil spring interposed between the main body and the control piece and wound around the outer circumferential surface of the push rod to effect the spring action in the direction opposite the forwarding direction of the push rod. The spring action of the coil spring causes the control piece to turn around a point supported by the supporting plate so that the control piece inclines with respect to the axial direction of the push rod with the result that an circular edge portion of the control opening is frictionally engaged with the outer circumference of the push rod. In this case, when the push rod is forwardly pushed by the driving unit, the push rod is allowed to move because the coil spring is compressed. However, when the push rod is moved in the direction opposite the forwarding direction, the movement is prevented due to the frictional engagement between the control opening and the outer circumferential surface of the push rod. Accordingly, when an operator operates the lever, the push rod is pushed forwardly whereby the gap-filling material is extruded from the nozzle formed at the front end of the tubular container. On the other hand, when the operator stops the operation of the lever, the lever returns to the original position together with the driving piece by the spring action of the coil spring, while the push rod is retained at the forwarding position due to the frictional engagement with the control piece of the control means.
Thus, in the conventional extrusion device, when the forwarding movement of the push rod is once stopped, the push rod is retained at a position of stop by the control means. For instance, after completion of work for filling a gap between a pair of panels, when operation of the driving means is stopped, the push rod is retained at the stopped position. Then, when the driving means is operated for filling a gap in another pair of panels, the gap-filling material in the tubular container is immediately extruded from the nozzle. In this case, however, there has been frequently occurred unwanted discharge of the gap-filling material, namely, the gap-filling material in the tubular container is slowly extruded from the nozzle even though the operation of the driving means is stopped to stop the extrusion of the gap-filling material. The unwanted discharging phenomenon for the gap-filling material remarkably takes place as viscosity of the material is high. The unwanted discharge of the gap-filling material causes contamination of an object to be worked when application of the gap-filling material is stopped due to a trowelling treatment, masking with a tape and so on. There also takes place contamination of a floor surface and devices in the vicinity of the object to be worked when the operator moves another place for working and contamination of clothes of the operator and the operator himself. Further, it causes loss of the gap-filling material. In addition, when the gap-filling material contains organic solvents, there takes place problems of firing and working conditions for laborors.
According to study by the inventors of the present invention, unwanted discharge of the viscous material such as the gap-filling material is caused owing to an inner pressure of the tubular container and viscoelasticity of the viscous material in the case that operation of the driving means is stopped to retain the push rod at a position of stop by means of the control means in the extruding of the viscous material in the tubular container. Further, according to study by the inventors, it has been found that when the viscous material is to be filled in the tubular container, air remains inside the tubular container, especially in the vicinity of the slidable bottom due to viscosity of the material. The air is compressed by the forwarding movement of the push rod. When the movement of the push rod is stopped, expansion of the compressed air and viscosity of the material slowly extrudes it from the nozzle.
In a case that a tubular container is formed integrally with the extrusion device main body, it is unavoidable that air remains in the tubular container when viscous material is sucked or filled in the tubular container from its end portion after viscous material previously filled in the container has been exhausted.
In a case of the extrusion device in which a cartridge type tubular container filled with viscous material is fitted to the extrusion device main body, it is unavoidable that some amount of air remains at a circular edge portion of the slidable bottom and inner wall of the tubular container because the viscous material is filled in the tubular container in a string form due to its viscosity when the viscous material is packed in the container. Accordingly, it is impossible to remove the residual air from the cartridge type tubular container before use of it. Further, it has been found that it takes much time to fill the viscous material in the cartridge type tubular container without leaving air in it and that it is impossible to evacuate air remaining in the cartridge type tubular container for a relatively short time without causing hardening of the viscous material.